The probes will lift off in an unmanned Delta II Heavy
Rocket and will start its three month journey to the moon. NASA’s Apollo
Astronauts used the Saturn V Rocket and covered the approximately 386,242
kilometres to the moon in a mere three days.The ‘more economical’ rocket launch brings the cost of the mission from
start to finish to US$ 496 million dollars.

Shortly after lift off the probes will separate from each
other and travel independently to the moon. Grail-A will arrive at the moon on New Year’s
Eve with Grail-B arriving on New Year’s Day. They will go into orbit around the
lunar poles and effectively chase one another around the moon. The probes will
range in distance apart from each other from 64 kilometres to 225 kilometres.
They will be bouncing radio signals between them providing their exact
locations, even on the far side of the moon.

When the mission ends in late spring (northern hemisphere),
Grail-A and Grail-B will be within 16 kilometres of the moon’s surface. Barring
any changes, they will then eventually crash into the moon.

The mission aims to create the most precise lunar gravity
map ever. Scientists are hoping to figure out what is beneath the lunar
surface, all the way to the core. The moon actually has the most uneven
gravitational field in the solar system, according to NASA. The moon’s gravity
is about one-sixth or Earth’s pull.

Scientists will be able to measure even the slightest variations
in the gap between the orbiting probes every single second. These changes as
subtle as they may be will indicate shifting masses below the lunar surface:
mountains in some places, lava tubes and craters in others. The probes will
also help pinpoint the best landing sites for future explorers, whether human
or mechanical.

A plan to put man back on the moon was scratched off in
favour of an asteroid and Mars. There are three spacecraft currently orbiting
the moon, making science observations. Since the Space Age began in 1957, 109
missions have targeted the moon. 12 men have walked on its surface in six separate
landings. 342 kilograms of rock and soil has been brought back to earth and are
still being analysed.

The launch of the GRAIL probes will be NASA’s second robotic
mission since the end of the shuttle programme in July. A probe names Juno is
headed for Jupiter following a successful launch on August 5. If the GRAIL is
not launched on September 8, the mission’s launch period lasts until October
19.